8-Bromoadenosine 3':5'-cyclic monophosphate, when used in association with an auxin, can completely replace the cell-division-promoting activity of either a cytokinesin or a 6-substituted adenylyl cytokinin in excised tobacco pith parenchyma tissue. The 8-bromo derivative of adenosine 3':5'-cyclic monophosphate was found to be far more resistant to degradation by plant adenosine 3':5'-cyclic monophosphate phosphodiesterases than was adenosine 3':5'-cyclic monophosphate. These findings appear to provide further support for the suggestion made earlier that the cytokinesins, which are potent inhibitors of both plant and animal adenosine 3':5'-cyclic monophosphate phosphodiesterases, exert their cell-division-promoting effects as regulators of adenosine 3':5'-cyclic monophosphate.